We examine Democrats’ decline in the House of Representatives from the mid-1930s to the late 1940s. Debates over American exceptionalism in the realm of social policy pay surprisingly little attention to a profound transformation that occurred during and after World War II: on the international stage, the United States emerged as the hegemon; at home, the Pentagon became the largest and most powerful agency in the federal bureaucracy. In modeling electoral losses suffered by Democrats, we show that World War II mobilization played an important role. First, Democrats lost ground in congressional districts where the nascent military-industrial complex was created, specifically in aircraft manufacturing centers. Second, the impact of aircraft manufacturing intersected with wartime in-migration of non-whites. Democrats suffered significantly greater losses where both non-white population and aircraft manufacturing employment increased. Our findings corroborate accounts of the social welfare state that stress partisan control and path dependence. Conservative congresses of the immediate postwar years left an imposing legacy, making it difficult to establish social welfare reforms for decades to come. Whereas most accounts of the rise and fall of the New Deal emphasize different aspects of domestic processes, we demonstrate that militarism and expansion of national security agencies undermined congressional support at a critical juncture. This intersection of wartime mobilization and social policy—and not an inherent and enduring institutional impediment to social welfare—contributed to underdevelopment of the welfare state and abandonment of universal social welfare programs in the United States.